As human hair becomes grey, for example, due to ageing or following a psychosomatic disorder, or is bleached due to excessive exposure to sunlight, a need can arise on the part of the consumer for a treatment to darken or to restore the color of the hair to its former appearance. Although it is possible to darken hair with a single treatment using, for example, an oxidative dye, the consumer usually prefers a gradual darkening treatment, so that the return to the original shade is not dramatic and therefore not noticeable to casual observer.
Direct dyes have been employed by Beecham Group PLC as described in GB No. 2 168 082 for dyeing hair using a composition containing, in addition to the dye, a cationic surfactant and a liquid carrier. These dyes are stated to include anthraquinone, azo, nitro, basic, triarylmethane or disperse dyes or any combination thereof.
In our attempts to develop a hair dye system which not only satisfies the desire of the consumer to obtain gradual darkening of the hair following repeated treatments over a period of weeks or months, while providing a rapid, even color change following each treatment, we have assessed the suitability for this purpose of a range of direct dyes, including basic dyes and neutral dyes. We were also concerned to provide a product that could be applied to the hair in the manner normally employed for shampoos and conditioners, without the need to wear gloves to avoid unacceptable staining of the hands with the dye.
Our experiments have shown that when using certain basic dyes, color uptake by the hair is rapid in that only a short treatment time of a few minutes is needed to achieve a moderate darkening of the hair, but that hand staining can occur to an unacceptable extent when the concentration of basic dye is sufficiently high to achieve adequate dyeing under these conditions.
We have also shown that when using certain neutral dyes, uniform dye coverage can be obtained, but the colour uptake by the hair is slower than with basic dyes, in that a longer treatment time is needed to achieve a moderate darkening of the hair. Furthermore, little or no hand staining is experienced with neutral dyes at concentrations sufficient to give adequate dyeing which is usually higher than that of the basic dye.
Accordingly, by using a product containing both a basic dye and a neutral dye, at carefully controlled concentrations, together with a cationic surfactant, which is present in the form of a disperse lamellar liquid crystal phase, we have discovered that it is possible to achieve rapid, uniform dyeing of the hair to a degree which satisfies the needs of the consumer desiring gradual darkening over a course of treatment as explained earlier, the product being suitable for application to the hair without the need to employ gloves.
Additionally, the cationic surfactant imparts a conditioning benefit to the hair which is retained after rinsing with water hair treated with this product.